High Quality Epitaxial Growth of Hexagonal GaN on Al2O3(0001) and Cubic GaN on GaAs(100) by Molecular Beam Epitaxy

Abstract

The growth of high quality GaN thin films of both hexagonal (h-GaN) and cubic phase (c-GaN) was achieved by molecular beam epitaxy. An ultra-thin amorphous GaN buffer layer was used to obtain a high quality h-GaN film on Al2O3(0001). Near-band edge emission (I2 and DAP) dominated the observed photoluminescence spectrum, and the full width at half maximum of the X-ray rocking curve was 9.8 arcmin. P-type conductivity was successfully achieved by Mg doping of h-GaN film with a hole concentration of 3 × 1017 cm–3 and a hole mobility of 27 cm2/Vs. With Si doping, it was found that the electron concentration could be controlled between 1019 and 1021 cm–3 by the Si cell temperature. For c-GaN growth on GaAs(100), a high phase purity was realized by using a newly introduced AlGaAs buffer layer technique. It was found that the formation of an AlGaN surface by nitridation of an AlGaAs buffer layer is essential to grow a highly pure cubic phase GaN film. An X-ray diffraction peak attributable to secondary hexagonal GaN could not be observed in reciprocal space area mapping and pole-figure measurements.